1. Field of Invention
This invention relates to a rotary cone rock bit. More specifically, it is directed to an improved rotary cone rock bit that includes radially directed nozzles to provide a cross flow through the drill bit dome and, thereby, reduce the accumulation of mud and a method for accomplishing same.
Rotary cone rock bits use drilling fluid, or mud, as a lubricant. The mud circulates down through a drill string, into the rock bit body, through nozzles positioned at the bottom of the rock bit, and toward the bottom of the well bore. In soft formations, the nozzles are particularly useful because the relatively high pressure mud creates a turbulence within the hole and stirs up formation cuttings facilitating their circulation from the well bore. From the well bore bottom, the mud circulates back to the surface carrying formation cuttings therewith.
Typically, however, the rotary cones of a rotary cone rock bit define a dome or cavity between the cones. Drilling mud and formation cuttings accumulate within the dome. The accumulation forms a mud ball and becomes impacted. This process is referred to generally as "bailing." Balling reduces the efficiency of the drilling because a portion of the cutting energy is consumed when the rotary cones act on the impacted mud ball. Thus, eliminating balling results in greater drilling efficiency.
2. Related Art
A number of devices attempt to solve the problem of balling. Illustrative of such devices is U.S. Pat. No. 4,665,999 that issued to Shoemaker on May 19, 1987. Shoemaker discloses variable length three-cone rock bit nozzles that, due to their varying lengths, create a cross flow through the drill bit dome.
Another prior effort to design a rock bit that reduces balling is U.S. Pat. No. 4,687,066 that issued to Evans on Aug. 18, 1987. Evans shows a rock bit having axially mounted angled nozzles that create a downwardly spinning vortex within the drill cavity. The purpose of the vortex is to sweep cuttings away from the cutting surfaces.
A further prior effort to reduce balling is U.S. Pat. No. 4,687,067 that issued to Smith et al. on Aug. 18, 1987. Smith et al. reveals a cross-flow rotary three cone rock bit with extended nozzles that creates the cross flow by providing nozzles on only two of the three leg segments.
Though the above mentioned rock bit nozzles may be helpful in reducing balling, they can be improved to provide more effective and efficient cross flow through the drill bit dome and, thus, better reduce balling.